930 under Restoration

Hey guys, I have an 86 951 and have failed emissions 3 times.

The 2nd test scores read like this:

25/25 Test

HC ppm 162 allowed and read 175 FAIL
CO% 1.04 allowed and read 1.94 FAIL
NOx ppm 1163 allowed and read 935 PASS

50/15 Test

HC ppm 167 allowed and read 200 FAIL
CO% .94 allowed and read 1.82 FAIL
NOx ppm 1273 allowed and read 958 Pass

Ok, I put in Bosch wr8dc plugs which were 2
heat ranges hotter than were in it. The co adjustment screw on the air flow meter, I turned
counter clockwise 2 full turns and this time I
only failed on one NOx test.

Last test readings

25/25 Test

HC ppm 162 Allowed and read 138 PASS
CO% 1.04 Allowed and read .78 PASS
NOx ppm 1163 Allowed and read 1770 FAIL

50/15 Test

HC ppm 167 Allowed and read 139 PASS
CO% .94 Allowed and read .40 PASS
NOx ppm 1273 Allowed and read 1263 PASS

Can anyone make a suggestion as to what to do?
Should I take one of those turns on the AFM out?

Please Please help!

James86-951

Is your catalytic converter internals still there? I know the NOx will be off if the guts are compromised.

jabbadeznuts

One trick I know of is to get the engine HOT and then turn it off before it's your turn at the station. This can help with a more complete combustion of the fuel. Other than that, nothing I can sudgest besides a new cat or something drastic like that.

bader$

I agree to check the cat. When the hc and co went down it raises the combustion temps and produces nox. the only thing on our cars that takes care of nox is the cat.

930 under Restoration

Yeah the cat is still intact. I guess I adjusted the AFM to far. Maybe if I readjust it and bring the HC and Co back up a bit, the Nox will drop enough.

James86-951

The best thing to do is to find someone with a 4 gas analyzer and see what is happening. Are you sure the honeycomb is still inside the cat? Your CO and HC are about where mine was and I passed. (I thought for sure the PO had gutted the cat.)

If you do up the A/F mix, be sure to make a quick run down the freeway to get everything up to temp. That will be your best bet.

MHT

is your car chipped? most chips were developed before the advent of loaded emissions testing, I have found in several instances that it was necessary to replace the stock chips to get cars through the ASM tests. The chips advance the timing too far at light load and this timing advance increases the production of oxides of nitrogen. If there are any cooling system problems, if it runs too hot, NOx will also be high. Those CO readings are not too lean, particularly for after cat. readings. They should not be causing you any problems. Good luck, Mark T.

MHT

sorry, by replace I meant to reinstall the stock chips.

930 under Restoration

My car finnaly passed emissions!!! Thanks to everyone for their suggestions.

The car was chipped but I never did check the cat to see if it had been knocked out by the PO mainly because I didn't want to buy a new one anyway.

After that last test, which I posted the results, I put the recommended heat range plugs in it (Bosch Wr7dc), turned the mixture back 1 turn to richen it back up a bit to drop the NOx and I poured in 2 pints of Isopropyl alcohol to a half tank of gas and then drove it about 20 miles.

There was one person in line so I shut it off so it cooled down for 5 minutes before it got tested.

The HC and CO was a tad more than half of what was allowed and the NOx came in at less than half of what was allowed.

I dont know what effect the alcohol had but a few guys here on the board recommended it in some older posts.

Good to be driving the P-Car again!!
The Suburban is comfy but can be a real pain to park in Buckhead.